A rugged and physical presence, Thorn holds the distinction of having represented Australia at rugby league and New Zealand at rugby union.

Born in New Zealand, he re-located to Australia with his family when he was 9-years-old where he would go on to make his name with the Brisbane Broncos in Australia's National Rugby League competition. He also represented Queensland in the State of Origin and made his international debut for Australia in 1997.

In 2001, he switched codes and moved back across the Tasman Sea to join the Crusaders in the Super 12 and Canterbury in the National Provincial Championship. Initially picked to tour with the All Blacks later that year he withdrew from the squad due to doubts about his commitment to the 15-man game. However, he eventually made his All Blacks bow against Wales in 2003 and would go on to gain selection for the 2003 Rugby World Cup.

His status as a dual-code international saw him join Bill Hardcastle in the record books as only the second man to have represented Australia in league and New Zealand in union.

After securing the NPC title with Canterbury in 2004, he returned to rugby league in 2005 for a second successful spell with the Brisbane Broncos where he stayed for three years before opting for a switch back to union in 2007 with the Tasman Rugby Union.

Thorn went on to win the Super 14 title with the Crusaders in 2008 to ease the pain of losing two finals with the Canterbury-based franchise in 2003 and 2004.

In 2009, he re-signed with the New Zealand Rugby Union and Canterbury until 2011. And Thorn continued where he left off with a series of impressive performances throughout the Super Rugby season. Thorn continued to be an important player on the international scene and was one of New Zealand's players of the tournament as the All Blacks secured their second World Cup.

Thorn played in Japan after the World Cup before joining Leinster as an injury joker for the rest of the 2011-12 season.